IAS 8, Dec 2018 Fill Co

This is question 3 part a. I need help in understanding part ii as to why IAS 8 is applied here.

Fill is a coal mining company and sells its coal on the spot and futures markets. On the spot market, the commodity
is traded for immediate delivery and, on the forward market, the commodity is traded for future delivery. The
inventory is divided into different grades of coal. One of the categories included in inventories at 30 November
20X6 is coal with a low carbon content which is of a low quality. Fill will not process this low quality coal until
all of the other coal has been extracted from the mine, which is likely to be in three years’ time. Based on market
information, Fill has calculated that the three-year forecast price of coal will be 20% lower than the current spot
price.
The directors of Fill would like advice on two matters:

(ii) how to calculate the net realisable value of the coal inventory, including the low quality coal

Suggested Answer:

Future changes in the forecast market price or the processing and sale of the low
carbon coal may result in adjustments to the NRV. As these adjustments are changes in estimates, IAS 8 Accounting Policies, Changes in Accounting Estimates and Errors will apply with the result that such gains and losses will be recognised in the statement of profit or loss in the period in which they arise.
Kindly explain why IAS 8 will apply here.
Thanks in Advance!!